upstream: avoid double hashing of protos in CDS init

[rojkov]

Commit Message: upstream: avoid double hashing of protos in CDS init
Additional Description:
Currently Cluster messages are hashed unconditionally upon instantiation of ClusterManagerImpl::ClusterData even if their hashes are known already.
Calculate the hashes outside of ClusterManagerImpl::ClusterData ctor to make use of already calculated ones.
Risk Level: Low
Testing: unit tests, manual tests
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A
Contributes to #12138

[alyssawilk]

code LGTM but given all your improvements in this space what do you think about adding a benchmark (and/or commenting benchmark improvements in the perf PRs)?

[yanavlasov]

code LGTM but given all your improvements in this space what do you think about adding a benchmark (and/or commenting benchmark improvements in the perf PRs)?

I'm planning to take over and complete PR #14167 for adding benchmarks. This is actually quite visible on internal CPU profiles at 7%.